Split cycle engines have been described in my U.S. Pat. Nos. 3,408,811 and 4,186,561. It has been found in practical experience with engines of the construction described in U.S. Pat. No. 3,408,811 that the high gas pressures in the combustion chamber during ignition require higher electrical potentials to be applied to spark plugs than in conventional internal combustion engines, with the result that the working life of the spark plugs is shortened.
U.S. Pat. No. 4,186,561 was directed to avoiding this difficulty by using ignition means other than spark plugs. Spark plugs, however, permit the timing of ignition in a particularly convenient manner, and equipment for use with them is already available on the market.